1. Field of the Invention
This invention relates to a method for repairing an HFC refrigeration system. More particularly, this invention relates to repairing a sealed refrigeration system in a household refrigerator which contains an HFC refrigerant and a hygroscopic lubricating oil, by making the repair after the refrigerant has been removed, providing an activated alumina filter and molecular sieve dryer in series in the liquid line, removing air from the system and then charging the system with fresh HFC refrigerant.
2. Background of the Disclosure
Hermetically sealed refrigeration systems are used for refrigerators, freezers, home and automotive air conditioners and the like. Such refrigeration systems include a compressor, a condenser and an evaporator, with a liquid refrigerant line containing an expansion device such as a capillary tube, orifice or thermal expansion valve between the condenser and evaporator. Refrigerators and freezers employ a capillary tube as the refrigerant expansion device and they also contain a dryer in the liquid line upstream of the capillary tube. In operation, the compressor compresses the refrigerant vapors which then condense to the liquid state in the condenser and pass through the liquid line and capillary tube into the evaporator. The capillary tube serves as an expansion valve. The refrigerant vaporizes in the evaporator, thereby absorbing its latent heat of evaporation from the surrounding environment, which provides the cooling. A desiccant dryer is frequently employed in the liquid line to absorb any moisture introduced into the system during manufacture, from leaks, and from repairs which open the system to the atmosphere. With refrigerators, freezers and nonautomotive air conditioners, the compressors are designed such that the compressor and electric compressor motor are in the same housing. Consequently, both the refrigerant and lubricating oil have to be miscible with each other and not form separate phases throughout the entire working temperature range of the system (e.g., -20 to +150.degree. F.). This also means that the refrigerant and oil are in contact with the coils of the electric compressor motor and must therefore be electrically insulative.
Typical refrigerants have included chlorofluorocarbons (CFC's), such as trichloromonofluoromethane and dichlorodifluoromethane known in the trade as R-11 and R-12, respectively, and hydrochlorofluorocarbons (HCFC's) such as monochlorodifluoromethane which is known as R-22. Compressor lubricating oils have generally been mineral oils which are hydrocarbon oils derived from petroleum and which are inexpensive, noncorrosive, relatively chemically inert, electrically insulative and hydrophobic. In making repairs to these systems the old refrigerant is removed, new refrigerant introduced and the system resealed. A desiccant dryer present in the liquid line removes moisture from the circulating refrigerant and oil to avoid icing of the capillary or expansion valve and also to avoid the formation of a corrosive mineral acid in the system, such as hydrochloric acid, by reaction of the water with the refrigerant. In the case of a compressor burn-out, polymer, wax, sludge and small amounts of fatty acids are sometimes formed which need to be removed from the system during a repair. When replacing a compressor, both the refrigerant and the lubricating oil in the system are discarded and replaced with a fresh charge. Typical repair procedures, desiccant dryers, and filters containing an adsorbent which have been used external of some systems for cleaning up old refrigerant and introducing the old refrigerant back into the system are well known and disclosed, for example, in U.S. Pat. Nos. 3,025,233; 3,175,342; 3,841,490; 4,554,792, and 5,247,812.
Many countries are prohibiting the use of CFC and HCFC refrigerants, because it is believed that the chlorine in the molecules has been a major factor contributing to the depletion of the ozone layer. Consequently, hydrofluorocarbon (HFC), chlorine-free refrigerants have been developed. These include CH.sub.3 CHF.sub.2, C.sub.2 HF.sub.5, CH.sub.2 F.sub.2, C.sub.2 H.sub.3 F.sub.3, CHF.sub.3 and C.sub.2 H.sub.2 F.sub.4 which are commonly known as R-152a, R-125, R-32, R-143a, R-23 and R-134a, respectively. R-134a which is 1,1,1,2-tetrafluoroethane (R-134 is its symmetrical isomer 1,1,2,2-tetrafluoroethane) has been adopted for use by many major manufacturers of refrigeration equipment in the United States. This R-134a refrigerant is not compatible with mineral oils and new synthetic oils have been developed which are very hygroscopic and form organic acids if exposed to moisture. These acids are corrosive and difficult to remove from the system. Some major manufacturers of refrigeration equipment have therefore recommended that once the hermetic seal has been opened, neither the compressor nor the system should be left open to the atmosphere for more than ten to fifteen minutes and that any repairs to the system be completed within this ten to fifteen minute time period. It is difficult to repair a unit within ten to fifteen minutes and not all repairs can be accomplished within this time.